Automatic control system for angular and planar electrode orientation



3,542,996 NAR .3 Sneets-Sheet l NOV. 24, 1970 J BQLLINGER ETAL AUTOMATICCONTROL SYSTEM FOR ANGULAR AND ILA ELECTRODE ORIENTATION 1966 OriginalFiled April 18,

NOV. 24, 1970 J BQLLlNGER ET AL 3,542,996

AUTOMATIC CONTROL SYSTEM FOR ANGULAR AND PLANAR ELECTRODE ORIENTATIONOriginal Filed April 18, 1966 3 Sheets-Sheet $3 Z DISTANCE BETWEEN PROBEELECTRODE (IN) L 8 RADIUS OF CURVATURE (|N.)

INVENTORS JOHN G. BOLL/NGER HOWARD L.HARRI5ON BY MICHAEL A. snmxsy /MAM,Msi/M 3,542,996 NAR Nov. 24, 1970 J BOLUNGER ETAL AUTOMATIC CONTROLSYSTEM FOR ANG ULAR AND PLA ELECTRODE ORIENTATION Original Filed April18, 1966 3 Sheets-Sheet L5 ma k6 um u WFL Rm 5 m f m 8 H m NM w 7 w R vfmxmw m U n T m no 5M P1 8 9 m [I 7. Z

United States Patent US. Cl. 219-125 5 Claims ABSTRACT OF THE DISCLOSUREAvweld electrode tracking system for welding overlapping edges includesa water cooled copper probe riding on one edge. The probe is pivotallymounted and extends to within .12 to .78 inch of the are. A linearvariable differential transformer has a spring loaded core engaging theprobe and generating analog voltage connected to energize an electrodemotor for positioning the electrode with respect to the workpiece. Anindependent signal source includes a cam curved in accordance with theangle in the weld plane and a follower to maintain the proper angle atwhich the electrode is fed to the weld arc.

This invention is directed to an automated control system for high speedarc welding, and more particularly to a weld seam tracking system forautomatically guiding a welding nozzle along a weld seam.

This is a divisional application of the application entitled AutomatedControl System For High Speed Arc Welding filed Apr. 18, 1966, with Ser.No. 543,160, and now Pat. No. 3,452,180, granted June 24, 1969.

A water cooled copper probe is disposed in very close proximity to theare for sensing incipient changes in the seam contour of the workpiece.The changes in the seam contour are substantially immediately convertedinto electrical signals which are transmitted by means of an electricalcontrol circuit to a motor means to produce compensating motions of theelectrode holder to guide the arc along the seam being welded. The probeemployed in the apparatus of the invention is disposed at a minimumtarget angle in relation to spatter generated by the are. It is watercooled to withstand extremely high arc temperatures and to immediatelyfreeze spatter which does contact it to therebyprevent spatteradherence.

The probe is provided with a linear variable differential transformerwhich converts seam tracking motions of the probe into electricalcontrol signals. The control signals are then transmittedinstantaneously to electric motor means for moving the electrode holdera distance and direction corresponding to the signal to maintain the arcin correct position relative to the workpiece for welding a non-linearseam. The control system requires no memory circuit and, in addition,applicant provides an independently operated electrode attitude controlmeans to insure and maintain the correct angle of incidence between theworkpiece and the electrode.

' Many different electrode guide systems have been proposed in the past,but most of these have proved impractical in actual use due to therequirement of costly memory and time delay circuits, and because ofshort seam tracer life due to arc spatter and overheating. Prior toapplicants invention, no probe system was available which could operatebest at distances less than three inches from a consumable electrodeare. No prior patent solved the problem of providing a continuous,smooth tracking motion which is capable of guiding an electrode holder3,542,996 Patented Nov. 24, 1970 around very close radii with minimalerror by means of an electromechanical, single-edge sensing devicecapable of correcting either plus or minus seam contour changes to anequilibrium condition.

The patent to Morehead 3,171,012 discloses a weld seam tracking systemwhich appears superficially similar to applicants invention. Thatsystem, however, operates on incremental signals, and must be disposedin a groove having a pair of edges in order to track at all. Moreheaddeflects a fulcrumed probe between a plurality of contacts which thenautomatically drive the electrode in a predetermined direction untilanother counteracting signal is received from deflection of the probe ina different direction. The fulcrumed probe provides only an on," offcontact signal.

This invention provides sensor means to sense and track a weld seam orother similar work line and establish a control signal means forangularly orienting the weld electrode or other tool member about anaxis to establish and maintain a selected optimum angular orientationwith respect to said seam. In accordance with one aspect of thisinvention a cam member is provided with a profile related to the path ofthe work line profile and the required changes in the angularorientation of the tool member. A cam follower is coupled to move withthe tool member and is correspondingly positioned by the cam. The camfollower is connected to a signal generator and provides a relatedcontrol signal which is connected in a drive for positioning of toolmembers.

Applicants apparatus provides accurate seam following on all types ofWeld seams and workpiece configurations, and requires no memory systemto store the electrode guiding signals. The system is inherentlyinfinitely variable, and not incremental in its guiding ability.

The drawings illustrate the presently preferred method of carrying outthe invention.

In the drawings:

FIG. 1 of the drawings is a side elevation with parts broken awayshowing the apparatus of the invention generally;

FIG. 2 is an enlarged plan view with parts broken away of the weldinghead and probe taken from lines 2-2 in FIG. 1;

FIG. 3 is an enlarged end view with parts broken away of the apparatusshown in FIG. 2 taken along lines 3-3 of FIG. 1;

FIG. 4 is a schematic diagram illustrating the effect of electrodeattitude angle and probe-to-electrode distance for a given radius ofcurvature on the X attitude error;

FIG. 5 is a schematic diagram showing the corrective effect accomplishedby changing the attitude of the Welding nozzle to the workpiece and alsothe residual Y curvature error;

FIG. 6 is a graph showing Y as a function of the actualprobe-to-electrode distance and radii of curvature;

FIG. 7 is a schematic diagram showing the sequencing circuit, thecontrol loop network and the carriage m'otor circuit; and

FIG. 8 is a schematic diagram showing the attitude control circuit forestablishing the optimum angle of incidence between the weldingelectrode and the Workpiece.

As shown in the drawings, an automatic welding assembly 1 includes aframe 2, a welding head 3, a Welding head carriage assembly 4 and awelding head control assembly 5. The welding head 3 includes a weld seamprobe transducer assembly 6 which is rigidly connected to the weldinghead 3 adjacent its lower end. The probe transducer assembly 6 and theWelding head 3 are both disposed on a support bar 7, which is connectedthrough a rotatable gear 8 to a carriage lead screw 9. Lead screw 9"isrotated to raise and lower the probe transducer assembly 6 and weldinghead 3 in relation to a workpiece 10.

" The rotatable gear 8 is connected to a pivot motor 11, which iselectrically connected to a cam control assembly 12 through electricalleads 13. Signals from the cam control assembly 12 operate motor 11 torotate gear 8' and support bar 7 to change the attitude of the probetransducer assembly 6 and welding head 3 relative to workpiece edge 14being welded. A control cam 15 of a particular design is used to keepthe attitude of the welding head 3 in correct relation to edge 14 tomaintain optimal welding conditions.

The weldingassembly lincludes, in addition to the above described parts,a motor drive 16 which includes a drive motor 17 having a pulley 18 andconnected to the carriage assembly 4 to drive the carriage assembly 4,the probe transducer assembly 6, and the weld head 3 along the seam tobe welded.

. The weld head 3 and probe transducer assembly 6 are suspended from thecarriage assembly 4 by means of the lead screw 9 through a carriage leadscrew housing 20. The carriage assembly 4 includes rollers 21 which rideon a track 22 disposed along the upper surface of the frame 2. A servomotor 23 disposed on the carriage assembly 4 is connected to rotate thelead screw 9, thereby raising or lowering the weld head 3 and probetransducer assembly 6.

The cam control assembly 12 includes a spring loaded cam roller 24 whichrolls along the pitch control cam 15 during welding. Control cam 15 ispreselected to provide electrical signals to pivot motor 11 through theactuation of a potentiometer 25. These signals cause pivot motor 11 toadjust the attitude of the weld head 3 and probe transducer assembly 6relative to the edge 14 to provide an optimal Welding angle throughoutthe welding procedure and with a minimum tracking control error betweenthe probe transducer assembly 6 and the weld head 3.

The welding head control assembly receives error signals from the probetransducer assembly 6. These error signals are electrical, and arereceived in an AC- DC transducer converter 26 where a DC error signal isestablished. This DC error signal is fed through an amplifier 27 whereit is amplified and transmitted as an AC correction signal to the servomotor 23 which rotates the lead screw 9. In addition, a tachometergenerator 28 is provided on the servo motor 23 to provide a variablefeedback signal to the amplifier from the servo motor 23, therebyproviding additional stability for the servo drive by smoothing thesystems response to error signals. The electrical sequencing circuitwill be described more in detail below.

' The most important feature of the subject invention is the probetransducer assembly 6. This assembly 6 includes abracket 29 whichsupports a water cooled copper probe member 30 thereon. The probe member30 includes a stylus 31 releasably secured to the main body of the probemember 30. The body of the probe member 30 is pivotally secured at itsend remote from welding head 3 to the bracket 29 so that the probemember 30 and the stylus 31 can move to follow edge 14 being welded.

The bracket 29 also provides mounting means for a small linear variabledifferential transformer 32 which has a' movable core 33. A sensing rod34 extends into the core'33 of the transformer 32. The sensing rod 34 ispreloaded against the upper surface of the pivoted probe member 30 bymeans of spring 35 and moves in response to movements of the stylus 31.Movement of the rod 34 moves the core 33 in transformer 32, therebycreating an AC error signal which corresponds to the deviation ofedge'14. The signal ultimately causes the movement of the welding head3'either up or down in relation to edge 14. When the welding edge 14 isnot irregu= 4 lar and the stylus 31 senses 0"c'hange, the'transformer 32produces a 0 error signal and the lead screw 9 does not rotate. Theelectrode 36, therefore, continues to track in a straight path alongedge 14.

The distance between the stylus 31 and the tip of the electrode 36should be as close as possible to obtain the most desirable tracking byelectrode 36. As illustrated in FIG. 5, the amount of curvature error,AY, is a function of Z, which is the distance between the tip of thestylus 31 and the electrode 36. As set forth in the graph in FIG. 6, itcan be seen that increasesin the radius of curvature for a specificvalue of Z produce a curvature error distance AY. The smaller the valueof Z for a given radius of curvature, the smaller is the error AY. Ascan be readily seen in FIG. 5, decreases in the distance Z significantlydecrease AY, and therefore, the amount of error. The probe-to-electrodedistance should be less than three inches in all processes utilizing theinvention, and it has been determined that a probe-to-electrode distanceranging from .12-.78 works best, with the smaller distance beingpreferred.

FIG. 5 shows the additional reduction in tracking error gained bychanging the attitude of the welding head 3 in relation to the workpiece10. As can be seen, the most desirable attitude for the welding head 3is an attitude in which the radius of curvature intersects the workpieceedge 14 at a point midway between the tip of stylus'31 and the electrode36 and with the welding head disposed perpendicularly to a line tangentto the edge 14 and intersecting the point on the radius of curvature asbest shown in FIG. 5. It can be seen that attitude control actuallytends to cancel out any attitude and curvature errors.

The invention is well adapted to use with a continuous, consumable barecarbon steel electrode 36 fed from a coil (not shown) and shielded atthe arc by C0 gas supplied through gas nozzle 38. This processinherently generates a relatively large quantity of metal spatter due tothe violent arc action as the consumable electrode 36 is burned off inthe CO shielding gas.

The probe transducer assembly 6 is designed to be particularly adaptableto operation in a high spatter environment. The probe member 30 isprovided with water cooling through the water hoses 39 connectedthereto. As mentioned above, the member 30 is copper, and is selectedfor its excellent heat transfer characteristic. Spatter striking thewater cooled probe member 30 and stylus 31 is cooled instantly, freezesand does not adhere to the members 30 and 31. Other materials havinghigh thermal conductivity and high diffusivity could be used in thestylus 31 and probe member 30. For example, both gold and silver couldbe used, as well as other alloys having the required thermalconductivity.

The stylus 31 is disposed at a very low angle with the workpiece edge 14and a relatively large angle relative to the axis of electrode 36 sothat stylus 31 presents a minimum target angle for spatter generated atthe arcing tip of electrode 36. As can best be seen in FIG. 2, the majorportion of the are generated spatter 40 is violently ejected from thearc along generally straight paths falling within a solid cone 41 havingits apex in the arc. There is an annular region between the spatter cone41 and workpiece 10 which is relatively spatter free. As can best beseen in FIG. 2, the stylus 31 isangularly disposed in this spatter-freeregion between the workpiece 10 and the spatter cone 41. The stylus 31extends to within about .25" of the arcing tip of the electrode 36 andis connected at its other end to the water cooled probe member 30. Y

The most desirable minimum probe-to-electrode distances may be obtained,therefore, because of low angle disposition of the stylus 31 and becauseof the heat sink characteristics of the water cooled probe member 30.The

stylus 31 is maintained at a sufficiently low temperature to permit longperiods of generally continuous Welding because of the excellent coolingeffect of members 30 and 31. Because the stylus 31 and member 30 aremaintained sufiiciently cool and have excellent heat transfercharacteristics, spatter which does strike them quickly freezes, anddoes not adhere.

The transformer 32, although disposed relatively close to the arc, iscompletely shielded from spatter by the probe member 30. Because of thisshielding effect, it is possible to use a relatively short sensing rod34 to sense movement of the pivoted probe member 30 and transfer thesemotions into the movable core 33 of the transformer 32.

As shown in FIG. 7, the electrical control system includes a controlloop network 42 and a carriage motor circuit 43. The nozzle attitudescontrol circuit 44 is shown in FIG. 8 of the drawings. This lattercircuit will be described later. Interconnecting the control loop 42 andthe carriage motor circuit 43 is a sequencing circuit 45 which controlsand integrates the operation of the control loop network 42 with thecarriage motor circuit 43.

The control loop network 42 includes the linear variable differentialtransformer 32 and its movable core 33 which provides an infinitelyvariable analog voltage signal to the AC-DC transducer converter 26. Inaddition, the tachometer 28, the amplifier 27, a dummy signal source 48,a plurality of control relay contacts 49-57 are provided in the controlloop network 42. Control relay contacts 49-54 are normally open, andcontrol relay contacts 55-57 are normally closed. The amplifier 27, thetachometer 28 and the control relays 49-57 provide a desired analogsignal which operates the AC servo motor 23. The servo motor 23 isconnected to drive lead screw 9 clockwise or counterclockwise, dependingon the direction of rotation of the servo motor 23. Clockwise rotationraises the welding head 3 by causing the carriage lead screw housing 20to rise on the lead screw 9. The housing 20 connects at its upper end toa ball nut 57a, and is prevented from rotating by means of a slide (notshown). Movement of the welding head 3 returns the movable core 33 tothe null position.

The welding head 3 is thereby automatically carried closer to the edge14 through the action of lead screw 9 in response to error signals fromthe transformer 32. When the analog signal is null, the lead screw 9stops turning, and the welding head 3 will continue to operate at aconstant level in relation to edge 14 until an analog signal is againreceived due to deviation in the contour of edge 14, sensed by thestylus 31 and transmitted through the linear variable differentialtransformer 32. Actuating coils 58-60 are provided to close (or open)the contact relays 49-57 in the correct sequence determined by thesequencing circuit 45.

The carriage motor circuit 43 comprises a DC power supply 61, aplurality of relay contacts 62-68 and a field 69 in the drive motor 17.A variable resistor 70 is provided in parallel with motor 17 for dynamicbraking. The carriage motor circuit 43 is controlled by actuating coils71-73 in the sequencing circuit 45. More specifically, coil 71 actuatesnormally closed switch 63 and normally open switch 64. Actuating coil 72operates normally open switches 65 and 66 and normally closed switch 67.When coil 73 is energized, it opens normally closed switch 68.

A normally open main contact switch 74 is provided (line 1) to energizethe sequencing circuit 45 initially. Once energized, relay coil contact75 is closed and held closed by a relay coil contact 76 (line 1). Amaster off switch 77 (line 1) is also provided to de-energize thesequencing circuit 45 when desired. This switch is normally closed.

Energization of the coil 76 also closes main power switches 78 and 79 toenergize the main legs of the circuit 45. Power is now available to amain cycle start button 80 (line 2) which is normally open. Closingbutton energizes a cycle start relay coil 81 (line 2). The relay coil 81closes a holding contact 82 (line 2), which provides a current path tocoil 81 after button 80 reopens. Coil 81 also closes a plurality ofoperating contacts 83 (line 4), 84 (line 7), 85 (line 10), 86 (line 11)and 8-7 (line 12) to commence the operation of the welding apparatus.Closing of the contact 83 (line 4) provides current to energize therelay coil 58 (line 4), which, when energized, closes a contact 88 (line4) and contacts 49 and 50 in the control loop circuit 42 to place thetransducer 32 into the circuit. A third, normally closed contact 57 issimultaneously opened by the coil 58.

Assuming the stylus 31 is above the edge 14, the transformer 32 willdetect error and cause the welding head 3 to descend to bring the stylus31 in contact with the edge 14. When the edge 14 is contacted, and thestylus 31 is balanced through the transformer core 33 to a nullposition, the limit switch 89 (line 6) 'closes, thereby energizing timer90, provided limit switch 91 (line 5) has also been actuated to closecontact 92 (line 6) through the action of relay coil 93 (line 5). Thelimit switch 91 will ordinarily be actuated when the welding head 3 isat the far left side of the welding fixture as viewed in FIG. 1. Onceenergized, the coil 93 can be held in until the end of the cycle by thecontact 88 (line 4), which was actuated by the coil 58 (line 4).

The timer closes its associated timer contact 94 after a timed period.This action energizes relay coil 95 (line 7a-8), which closes thecontrol circuit (not shown) of the Welding head 3 to provide weldingcurrent, shielding gas and electrode feed to the electrode 36. When theenergized electrode 36 contacts the workpiece 10, an arc is struck andwelding commences.

Closing timer contact 94 also energizes the relay coil 71 (line 7),which is adapted to close normally open contacts 62 and 64 in thecarriage motor circuit 43. Coil 71 also opens normally closed contact 63in the carriage motor circuit 43, thereby removing variable resistor 70from the circuit to allow full current to be applied to the carriagemotor 17.

Welding now proceeds while the welding head 3 moving along edge 14 ofthe workpiece 10 and the stylus 31 contacting the edge 14 immediatelyahead of the electrode 36. As explained above, contour changes of theedge 14 displace the stylus 31, creating a DC error signal in thetransformer 32. This signal is converted through the control loopnetwork 42 into mechanical motion of the lead screw 9 driven by theservo motor 23, which receives an AC correction signal from the controlloop network 42.

Simultaneously, the nozzle attitude control circuit 44 is energized. Asshown in FIG. 8 of the drawings, the circuit includes the pivot motor11, the potentiometer 25, a feedback potentiometer 96, a stabilizingtachometer 97 and an amplifier 98. As mentioned above, the cam controlassembly 12 provides mechanical input signals to the potentiometer 25 asthe cam roller 24 rolls along the control cam 15. Control cam 15 hasbeen preselected based on the general contour of the workpiece toprovide a signal which is translated into an electrical signal bypotentiometer 25, amplified by amplifier 98 and fed to servo motor 11 tocause a mechanical input to gear box 8 to rotate support bar 7 theamount required to maintain the welding head 3 in the correctorientation for optimum welding conditions, and to minimize the errorsof probe member 30 as mentioned previously.

After the welding head 3 has moved across the frame 2 and welding hasbeen completed, stop cycle limit switch 99 (line 9) is actuated. Asecond limit switch 100 (line 7) is also opened. Opening of switch 99de-energizes the welding circuit (not shown) and welding stops. Also, aholding coil 101 (line 9) is energized to open a normally closed contact102, thereby de-energizing the cycle start relay coil 81 (line 2). Thisoperates the contacts 83 (line 4), 84 (line 7), 85 (line 10), 86 (line11) and 87 (line 12)" to reopen contact 83 and reclose contacts 8487.Acontact 103 (line 8) is also reopened by de-energizing the coil 81(line 2). Opening contact 103 de-energizes coil 95 (line 8) and itsassociated contact 97 reopens. Opening of contact 97 insures that nocurrent will flow through any portion of line 8 unless timer contact 94recloses.

At the same time, a relay contact 104 (line 6) is .reopened, therebytie-energizing timer coil 90 (line 6). Timer contact 94 reopens andthereby assures the cutoff of current flow through either line 7 or 8,because contact 97 (line 8-) has opened, as mentioned above. With line 7de-energized, the coil 71 is de-energized, thereby reopening contact 62and 64, and reclosing contact 63 in the carriage motor circuit 43 tostop the carriage motor.

As mentioned, closing of the limit switch 99 (line 9) energized coil 101to open normally closed contact 102 (line 2). Coil 101 also closesnormally open contact 105 (line 10a) to energize relay coil 59 (line 10)which thereupon close-s contacts 51 and 54 and opens contact 56 in thecontrol loop network 42 to throw a dummy voltage signal onto motor 23from dummy voltage signal source 48. This signal rotates lead screw 9 toraise welding head '3 to the starting position preparatory to repeatingthe Welding cycle. The dummy signal controls the motor 23 at this point,because contacts 49 and 50 have reopened, isolating the transformer 32from the loop control network 42. When the point is reached wherewelding head 3 should stop its upward motion, a stop limit switch 106(line 12a) is closed to energize the relay coil 72 (line 12). This openscontact 104a (line 10) to de-energize coil 59 (line 10) thereby removingthe dummy voltage signal source 48 from the control loop network 42 andstopping the raising of welding head 3.

Energizing the relay coil 72, in effect, also opens a contact 107 (line9). This de-energizes coil 101 (line 9) and thereby reopens contact 105(line 10a) so that coil 59 is de-energized both through line 10 and 10a.Coil 72 also closes contacts 65 and 66 in the carriage motor circuit 43to drive the welding head 3 to the left. A normally closed contact 67 isopened by coil 72 to remove the variable resistor 70 from the circuit 43of the motor 17 to permit a full speed return to the weld startposition.

When the welding head 3 has returned to the far left position, itactuates the limit switch 91 (line which deenergizes coil 93 (line 5),opening a contact 109 (line 12.). This de-energizes coil 72, openingcontacts 65 and 66 in the carriage motor circuit 43 and stopping thewelding head 3 at the far left position, where the cycle may now berepeated.

Manual control can be incorporated into the system, of course. Forexample, pushbutton controls 110-113 for UP, DOWN, LEFT and RIGHTmotions can be added to lines 10, 11, 12 and 7 respectively. Otheradditional pushbutton controls can be added to stop the cycle at anypoint and continue as desired. For example, a STOP button 114 isprovided to energize coil 73, which, when energized, opens normallyclosed contact 68 in the carriage motor control circuit 43 and cuts offthe carriage motor 17. Actuation of the coil 73- also closes a normallyopen contact 115 (line 13a) to hold the line 13a13 in the circuit whenbutton 114 again opens. A second normally closed contact 116 (line 13)is provided in line 13, and is opened by depressing a CONTINUE button117 (line 14) which energizes a relay coil 118 (line 14). Thiscoil opensnormally closed contact 116- to permit normally closed contact 68 toagain close upon de-energizing of its coil 73.

I A STOP-RETURN button 119 (line 3) can be provided which is depressedto energize a relay coil 120 (line 3). The relay coil 120 closesnormally open contact 121 .(line 9a) to energize relay coil 101 (line 9)even when the limit switch 99 is open. In this way, the cycle may bestopped through operation of the coil 101, etc., without first closingthe limit switch 99. :In addition,

coil has a holding contact 122 around the button 119 to hold the circuitin after the button 119 reopens. A limit switch 123 (line 3) is alsoprovided which will close to energize coil 120 even when the button 119is not de pressed. The limit switch 123 is disposed on the welding head3 to be closed when the welding head 3 reaches its bottom limit oftravel. When limit switch 123- closes, it also stops the weld cycle andcommences the return cycle. Normally closed contact 124 (line 3) can beprovided to disenable line 3 when the limit switch 91 has beenenergize-d, thereby energizing coil 93 which opens switch 124. Anormally closed contact 125 (line 7) is also provided to disenable theright movement whenever the relay coil 72 is energized, thus insuringthat when the carriage motor is to be driven to the left, no currentwill flow to short out the then open switches 62 and '64 in the carriagemotor circuit 43. A similarly functioning normally closed contact 126(line 12) is provided to insure that coil 72 will not be energized atthe same time coil 71 is energized to drive the carriage to the right.

Other additional controls can also be included, and will be readilyapparent. The description above is believed suflicient to fully pointout the operation of the invention and the nature of the advanceapplicants have made in automated seam welding.

The invention provides an accurate electromechanical automatic weldingsystem which provides accurate control of the welding head movementalong a contoured seam being welded. The system provides a substantiallyinstantaneous response to changes in direction of the weld seam to guidethe electrode along in the most optimum attitude for welding.

The probe tracking apparatus is disposed at a distance of less thanthree inches from the arc and preferably at about one-eighth of an inchto provide accurate tracking without requiring a memory system. Theprobe is resistant to are temperatures and is disposed below the spattercone to further enhance its useful life.

The apparatus utilizes a linear variable differential transformer toconvert the physical changes in the weld seam into an electrical controlsignal which is amplified and then fed to the welding head guide motorsto correct the position of the welding head back to a 0 error position.

We claim:

1. In a tool positioning control for positioning a tool member withrespect to changing the tool work path along a workpiece in a givenplane, comprising mounting means for said tool member, control meansconnected to said tool member for independently moving said tool memberalong a pair of perpendicular rectilinear paths in a given planeincluding said tool work path and including a transducer means incontact with the workpiece continuously and directly sensing themovement of said tool wonk path in one of said rectilinear pathsimmediately adjacent said tool member and establishing an electricalcontrol signal for positioning the tool member along the correspondingrectilinear path to maintain a fixed relationship within said pair ofrectilinear paths in said given plane and thereby to maintain the end ofthe tool member moving along said tool work path, drive means to rotatethe tool member about an axis perpendicular to said given plane forvarying the introduction angle of said tool member, generating meansincluding a cam having a profile corresponding to a preselectedintroduction angle of said tool member into said work path and a camfollower following said cam profile and coupled to an electrical signalmeans for establishing an electrical control signal corresponding tosaid preselected angle, and motor means coupled to said signal means andto said drive means to maintain the selected angular position of saidtool member as the tool member is moved in said two rectilinear paths.

2. The tool positioning control of claim 1, wherein said generatingmeans produces a signal related to a perpendicular relationship of thetool member and the work path for all positions along said work path.

'3. The tool positioning control of claim 1, wherein said generatingincludes means movable in accordance with the tool member forestablishing said signal.

4. The tool positioning control of claim 1, wherein said transducermeans includes a follower immediately adjacent the tool tip andsimultaneously moving along said work path in front of said tool member,said generating means establishes a signal related to a fixed angularrelationship of the tool member and the work path for all positionsalong said work path to maintain said tool member perpendicular to aline tangent to a point between said follower and said tool tip.

5. The tool positioning control of claim 1, wherein said transducermeans includes a diflferential transformer to establish a continuouscontrol signal for moving said tool member in said one path, and saidcontrol means including a means to support said tool member for fixedmovement along the second rectilinear path.

References Cited UNITED STATES PATENTS 2,288,032 6/1942 Smith 219-1252,839,663 6/1958 McCollam 219-76 2,927,992 3/1960 Bateman 219-1253,122,970 3/1964 Rhoades 336-30 X 3,150,624 9/1964 Brems 219-125 X3,158,121 11/1964 Brems 219-125 X 3,171,012 2/1965 Morehead 219-1243,408,475 10/1968 Pier 2.19-125 JOSEPH V. TR'UHE, Primary Examiner 15 L.A. SCHUTZMAN, Assistant Examiner US. Cl. X.R. 90-62; 228-7, 8

